For the purpose of reducing the weight of metal parts while giving them greater strength, especially in tension or in compression, it is known to incorporate ceramic fibres thereinto. For example, these are silicon carbide (SiC) fibres which have a tensile strength and a compressive strength that are substantially greater than that of a metal such as titanium.
The manufacture of these parts involves the prior formation of inserts from metal-coated ceramic filaments. They are also referred to as CMM fibres or coated filaments. The metal gives, in particular, the elasticity and flexibility necessary for handling them.
A known process for manufacturing such reinforced parts comprises the production of a winding of coated filaments around a mandrel. The winding is then introduced into a main metal body or container in which a slot forming the housing for the insert has been machined beforehand. The depth of the slot is greater than the height of the winding. A cover is placed on the container and welded to its periphery. The cover has a tenon having a shape complementary to that of the slot, and its height is adapted to that of the winding placed in the slot so as to fill the slot. Next, a hot isostatic pressing step is carried out, during which the cover is deformed and the winding is compressed by the tenon. The surface of the container along the edge of the slot is inclined so as to form a corner face for ensuring progressive deformation of the cover during the pressing phase.
The hot isostatic pressing technique consists in placing the part in an enclosure subjected to high pressure, of the order of 1000 bar, and also to high temperature, of the order of 1000° C., for a few hours.
During this treatment, the metal sheaths of the coated filaments are welded together and to the walls of the slot by diffusion welding, to form a dense assembly composed of a metal alloy within which the ceramic fibres extend. The part obtained is then machined to the desired shape.
The process serves for the manufacture of axisymmetric aeronautical parts, such as rotor disks or blisks (integrally bladed disks), but also non-axisymmetric parts such as connecting rods, shafts, actuator bodies and casings.
It is difficult to machine the slot in the main body, especially because of the small joining radii in the bottom of the slot between the surface of the bottom and the side walls. Such a small joining radius is necessary in order to house the insert with as small a clearance as possible, the insert having a rectangular cross section and being formed from small-radius filaments. The machining of the corresponding tenon in the cover is not easy either, because of the non-open-ended corners and because it is necessary to have a shape perfectly matching the slot.
The Applicant has developed a process for manufacturing parts of elongate shape that incorporate an insert with straight portions contributing to the transmission of the unidirectional tensile and/or compressive forces. This process is described in Patent Application FR 07/05453 of 26 Jul. 2007. The Applicant has also developed a process for manufacturing a straight insert. This process consists in producing an insert blank in the form of a winding, in compacting said blank in a container by hot isostatic pressing and then in machining the straight inserts in the compacted container. Such a process is described in patent application FR 07/05454 of 26 Jul. 2007.
However, when the parts to be produced are not axisymmetric, but are of oblong shape, with an oval shape or else of a shape with straight portions, precise adjustment over long lengths is difficult to achieve. This is even more difficult for inserts formed from very rigid coated filaments, because of the ceramic fibres that require the formation of housings in which they fit perfectly. The cover must be assembled perfectly in the slot so as not to let the fibres escape.
Instead of manufacturing the insert separately and then transferring it to the slot of the main body, Patent FR 2 886 290 in the name of SNECMA proposes, according to one embodiment, to produce the winding directly on the main body. Instead of a slot, two shoulders are provided in the body. The first one has a bearing surface for the direct winding of a coated filament. This surface is parallel to the winding direction. When the winding has been completed, the slot is reconstituted by placing a part on the main body which has a shape complementary to that of a second shoulder forming a step in relation to the first shoulder. The cover with the tenon is then positioned on the insert that has just been wound and the assembly undergoes a compacting operation. The manufacturing problem is only partly solved by this solution, since the assembly operation remains complicated.
Patent Application FR 07/09171 in the name of the Applicant specifies that the housing for the insert in the metal body has the form of a notch of L-shaped cross section, the cover having an internal notch of L-shaped cross section and of shape complementary to that of the metal body with said insert. Furthermore, the cover is shaped on the outside so that the compressive forces are exerted perpendicular to the faces of the notch.
Thus, the current manufacturing techniques make it possible to create metal parts that include one or more reinforcements made of metal-matrix composites from a winding of coated fibres and a container—a body and a cover. These structures are very effective but have a high manufacturing cost. In particular, the machining of the main body of the container with its cover represents a large fraction of the total cost of the parts.